var button:Button  = v.findViewById(R.id.button3)
val intent = Intent(Intent.ACTION_GET_CONTENT)
val mimeType = "audio/*"
val packageManager = activity!!.packageManager

首先宣告按鈕(Button)
Intent.ACTION_GET_CONTENT 代表可以從手機中選取數據
mimeType 設置成audio 代表音訊
packageManager

        button.setOnClickListener(View.OnClickListener {

            intent.type = mimeType
            val list: List<ResolveInfo> = packageManager.queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY)
            if (list.isNotEmpty()) { // 如果有可用的Activity
                val picker = Intent(Intent.ACTION_GET_CONTENT)
                picker.putExtra(Intent.EXTRA_LOCAL_ONLY, false)
                picker.type = mimeType
                // 使用Intent Chooser
                val destIntent = Intent.createChooser(picker, "選取MP3音樂")
                startActivityForResult(destIntent, 100)
            } else { // 沒有可用的Activity
                Toast.makeText(activity,"沒東西",Toast.LENGTH_SHORT).show()
            }